Gauge cover



March 25 1924.

G. D. MACBETH GAUGE COVER Filed April 21, 1925 2 Sheets-Sheet 1 FII3.1-

March 25, 1924. I 1,488,403

G. n. MACBETH GAUGE COVER Filed April 21, 1925 2 Sheets-Sheet 2 FIG.E|.

TNESS r O hum,

Patented Mar. 25, 1924.

UNITED STATES GEORGE D. MACBETH, F PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO MACBETH- EVANS GLASS COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

GAUGE COVER.

Application fled April 21, 1923. Serial No. 633,713.

, a citizen of the United States, and a resiii dent of Pittsburgh, Pennsylvania, in the county of Allegheny and State of Pennsylvania, have invented anew and useful Improvement in Gauge Covers, of which the following is a specification.

The invention relates to covers for liquid level gau es of the type commonly used'to indicate t e water level in liquid containers such as tanks, reservoirs, boilers and the like.

Gauges of the particular type herein contemplated comprise a metal casing and a transparent cover, usually of glass, clamped to it. Between the metal casing and the rear face of the cover there is a chamber which is placed in communication with the liquid container through suitable openings formed usually in the ends of the metal casing. A portion of the rear face of the gauge cover is provided with what is commonly known as a totally reflecting surface which, when backed with a medium of small index of refraction such as air or steam or other gases or vapors, reflects the light striking it, and by reason thereof appears brilliant when viewed from proper positions. However, when backed by a liquid medium such as water, the reflecting surface does not reflect the light, but, on .the contrary appears dark. Due to this, the portion of the gau e chamber occupied by liquid appears dar the portion occupied by 311791 steam appears brilliant in contrast with the dark portion, and the liquid level is indicated by the hori zontal line of division between the two.

As heretofore actually constructed, the

totally reflecting portions of the faces of gauge covers have terminated visually straight lines perpendicular to the longitudinal extent of the covers, that is to say lines which are visually' horizontal when the gauges are installed-for use. When no liquid is in a gauge chamber h'avin'g'fsluch a cover, the entire totally reflecting'sulrface appears brilliant, the portion of the aver below such surface a pears Idark,and the line between the bri "ant ;and" dark area s being horizontal indicates a false" liquid level. Furthermore, the totally reflecting portions of the faces have bee formed of what are commonly known .as totally reflecting prisms, the ends of eachlof which gradu- "jand the appearance of he ally taper to a oint, which has resulted in an objectionab e lack of sharpness in the water level indications at the lower end of the gauge. Due to the form of the terminations of the totally reflecting surfaces, explosions of steam-boilers have occurred because the engineers believed, when viewing the gauges, that water was in the boilers, whereas, in fact, the boilers had what proved to be disastrously small amounts of water in them.

The object of the invention is to provide a cover for liquid level gauges which will eliminate the possibility of a false or obscure liquid level being indicated.

The invention is illustrated in the accompanying drawings of which Fgi 1 is a face View of a complete gauge insta ed for use; Fig. 2 a vertical central sectional view taken on the line II-II, Fig. 1; Fig. 3 a horizon- .tal sectional view taken on the line III-III, Fig. 1,; Figs. 4, 5, 6 and 7 face views of the lower ends of gauge covers illustrati diflerent embodiments of the inventionyaiig Fig. 8 a transverse sectional view of a gauge cover illustrating a modification of construction. 7

As illustrative of the "general type of gauges contemplated herein, that shown in the drawings comprises a casing 1 provided at its upper and lower ends with openings bolts 7 extend into the casing. On cachSide of this cover, between it and casing 1 and damp mb th r a g -e e an 1 9 whichiseasl the gauge ch mber 4 and form a t h jd f th swe t r- Th Pr nings 2 .and 3' of the casing may be threaded for the attachment pf pipes 10 and 11' which used.

In Fig. 2 a body .of liquid. 12 is indicated as filling the lower portiOn of l4, g ug ,erdu by 1 steam or air above the ihquid is {inlb'y the shading .on Fig. ,1. The

to i s being backe in at t part .b

darkly h aea ortipn or the cover is the part of the totally reflecting portion backed by liquid, and also the margin of the cover outside of the totally reflecting portion. The line 13, marking the upper limit of the main shaded portion, shows the liquid level. \Vhen liquid fills only a portion of the gauge chamber this line is always horizontal.

According to this invention the rear face of the gauge cover 5, that is to say, the face adjacent to gauge chamber 4, is provided with atotally reflecting portion having its lower end terminating abruptly in a line which, when no liquid is in the gauge chamber, cannot be confused with the horizontal line 13. For this purpose, the lower end of the totally reflecting portion terminates in a line which is visually non-coincident with a line lying in the general plane of such surface perpendicular to the longitudinal extent of the cover, or, stated difl'erently, diflerent parts of the totally reflecting portion of the surface visually terminate in dilferent lines lying in the general plane of the reflecting portion and perpendicular to the longitudinal extent of the cover. As will presently be explained more in detail, the terminating line may have the appear ance of being curved, straight or irregular.

The totally reflecting portionof the surface is preferably'formedofa plurality of parallel totally-reflecting: abruptly-ending prisms 14 extending longitudinally of the gauge cover and inset in theUmaZnner shown in Fig. 3. However, the prisms qnayproject outwardly as shown in Fig. 8, andtthe totally reflecting portion may be formed :of rearwardly-projecting sharply-defined 'CUbB'zCOP ners 15 as shown in Fig. 7 lVhen the totally reflecting portion of the surface is formed by prisms l t in the manner explained, their .lower ends preferably so terminate as to appear as an outwardly extending curved line as indicated in Fig. 1 by the dotted line16; That the gauge cover may be symmetrical and used either end lowermost, the totally reflecting portion of the surface preferably terminates the same at both ends.

As illustrative of different manners of terminating the totally reflecting portion to avoid showing a false or obscure liquid level, the prisms are shown terminating so as to appear as an inwardly extending curved line 21 inFig. 4:, as a straight oblique line 17 in Fig. 5, and as an irregular line in Fig. 6. In

Fig. 7, the reflecting portion terminates in.

the irregular line forming the lower. boundary of the cube corners 15. In all cases differentparts of the totally reflecting portion of the surface terminate abruptly indifierent lines visually lying in the general plane of such surface perpendicular to the longitudinal extent of the gauge cover and hence in a line which is visually not coincident with any one of such perpendicular lines. This is illustrated in Fig. 6 wherein the totally reflecting prisms 14 are indicated as terminating in different lines 18 visually lying in the general plane of the totally reflecting portion and perpendicular to the longitudinal extent of the gauge cover. Furthermore, in all cases the totally reflecting surfaces terminate abruptly, and hence their ends are sharply The gauge cover is preferably formed of a body of transparent glass, but may be formed of other transparent materials, such for example as celluloid, mica or bakelite, which are sufliciently strong and resistant to the chemical action and the temperature of the fluids that come in contact with them.

Also, the gauge cover is preferably formed of chamber, the lower end of the brilliant total reflecting portion is indicated by a line which is sharply defined, and which, being other than horizontal, cannot be mistaken for a liquid level indication.

I claim:

1. A cover for a liquid level gauge, comprising an elongate body of transparent material having a totally reflecting portion on its rear surface terminating abruptly at its lower end in a line which is visually noncoincident with a line lying in the general plane of said surface perpendicular to the longitudinal extent of the cover, whereby the lower end of the totally reflecting portion of the rear surface is sharply defined in other than a horizontal line.

2. A cover for a liquid level gauge, com: prising an elongate body of transparent material provided with a totally reflecting por' tion on its rear surface having at one end thereof different parts terminating abruptly at their lower ends in different lines visually lying in the general plane of the reflecting portion perpendicular to the longitudinal extent of the cover, whereby the lower end of the totally reflecting portion of said surface is sharply defined in other than a horizontal plane.

3. A cover for a liquid level gauge, comprising an elongate body of transparent glass provided on its rear face with a pluralityof longitudinally extending. totally reflecting prisms each terminating abruptly at the lower end of the cover in a line which is visually non-coincident with a line lying in lar to the longitudinal extent of the cover,-

whereby the ends of the totally reflecting of said prisms terminating abruptly in a I prisms are sharply defined in other than a visually curved line at each end of the cover. 10

horizgntal ling. h d 1 1 In testimony whereof, I sign my name.

4. cover or -a ui eve gauge eom- 5 prisin an elongate bddy of transparent glass GEORGE MACBETH' provi ed on its rear face with a plurality of Witnesses: inset parallel totall reflecting prisms ex- HARRY S. Hownn,

tending longitudinal y of the cover, the ends PAUL N. CRI'rcnLow. 

